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We demonstrate |W〉 state encoding of multiatom ensemble qubits. Using optically trapped Rb atoms, the T2 coherence time is 2.6(3) ms for N=7.6 atoms and scales approximately inversely with the number of atoms. Strong Rydberg blockade between two ensemble qubits is demonstrated with a fidelity of 0.89(1), and with a fidelity of ~1.0 when postselected on a control ensemble excitation. These results are a significant step towards deterministic entanglement of atomic ensembles. [ABSTRACT FROM AUTHOR]

We demonstrate high fidelity two-qubit Rydberg blockade and entanglement on a pair of sites in a large two-dimensional qubit array. The qubit array is defined by a grid of blue detuned lines of light with 121 sites for trapping atomic qubits. Improved experimental methods have increased the observed Bell state fidelity to FBell=0.86(2). Accounting for errors in state preparation and measurement we infer a fidelity of F-SPAMBell=0.88. Accounting for errors in single qubit operations we infer that a Bell state created with the Rydberg mediated CZ gate has a fidelity of FCZBell=0.89. Comparison with a detailed error model based on quantum process matrices indicates that finite atom temperature and laser noise are the dominant error sources contributing to the observed gate infidelity. [ABSTRACT FROM AUTHOR]

Cooperators benefit others with paying costs. Evolution of cooperation crucially depends on the cost-benefit ratio of cooperation, denoted as c. In this work, we investigate the infinitely repeated prisoner's dilemma for various values of c with four of the representative memory-one strategies, i.e., unconditional cooperation, unconditional defection, tit-for-tat, and win-stay-lose-shift. We consider replicator dynamics which deterministically describes how the fraction of each strategy evolves over time in an infinite-sized well-mixed population in the presence of implementation error and mutation among the four strategies. Our finding is that this three-dimensional continuous-time dynamics exhibits chaos through a bifurcation sequence similar to that of a logistic map as c varies. If mutation occurs with rate μ≪1, the position of the bifurcation sequence on the c axis is numerically found to scale as μ^{0.1}, and such sensitivity to μ suggests that mutation may have nonperturbative effects on evolutionary paths. It demonstrates how the microscopic randomness of the mutation process can be amplified to macroscopic unpredictability by evolutionary dynamics.

We demonstrate low-loss measurement of the hyperfine ground state of rubidium atoms by state dependent fluorescence detection in a dipole trap array of five sites. The presence of atoms and their internal states are minimally altered by utilizing circularly polarized probe light and a strictly controlled quantization axis. We achieve mean state detection fidelity of 97% without correcting for imperfect state preparation or background losses, and 98.7% when corrected. After state detection and correction for background losses, the probability of atom loss due to the state measurement is <2% and the initial hyperfine state is preserved with >98% probability.